1. Field of the Invention
The present invention relates to a path setting apparatus and a path setting method that set a wireless communication path, a management apparatus and a management system that manage the set wireless path, and a computer readable storage device that has a program for realizing the path setting recorded therein.
Priority is claimed on Japanese Patent Application No. 2011-004751, filed Jan. 13, 2011, the content of which is incorporated herein by reference.
2. Description of the Related Art
All patents, patent applications, patent publications, scientific articles, and the like, which will hereinafter be cited or identified in the present application, will hereby be incorporated by reference in their entirety in order to describe more fully the state of the art to which the present invention pertains.
Conventionally, a distributed control system (DCS) where field devices such as a measurer and an operator and a management apparatus for managing and controlling the field devices are connected to each other through a communication bus is constructed in a plant or a factory to realize high automation. The conventional field devices mostly transmit and receive various signals such as a measurement signal and a control signal through a wired communication bus installed at the plant and the like. Recently, wireless field devices that transmit and receive various signals wirelessly in conformity with an industrial wireless communication standard such as ISA100 or WirelessHART have been realized.
ISA100 is a wireless communication standard for industrial automation that was devised by the International Society of Automation (ISA). Since ISA100 is the wireless communication standard used for measurement and control in plants, it is important to realize real-time responsiveness (minimize transmission delay (latency)). Therefore, in the standard of ISA100, a plurality of wireless access point devices (devices that perform wireless communication with the wireless field devices) are provided and the wireless access point devices and the wireless field devices are connected in a one-to-one relationship.
WirelessHART is a wireless communication standard that was proposed by the Highway Addressable Remote Transducer (HART) Communication Foundation of the United States. WirelessHART is based on a sensor network. The sensor network is a wireless network that allows a plurality of wireless terminals with sensors attached to be scattered in a space to make it possible for the wireless terminals to collect environmental and physical situations in cooperation with one another. For this reason, in the standard of WirelessHART, one wireless access point device is provided and a wireless network that is formed in a mesh shape by wireless devices such as a wireless field device and a repeater is connected to the wireless access point device. In WirelessHART, information showing the communication quality of each wireless device is collected by a management apparatus and a wireless path is dynamically switched based on the collected information. Japanese Unexamined Patent Application Publication No. 2009-111976 discloses technology for optimizing a wireless mesh network.
Because there are a plurality of industrial wireless communication standards, a vendor who provides a network infrastructure needs to design and develop a network infrastructure for each standard. In addition, an operator who uses the network infrastructure needs to conserve and manage the network infrastructure using different tools or techniques for each standard. For this reason, the burden of cost for both the vendor and the operator increases. Therefore, recently, a movement to unify the industrial wireless communication standards into one standard has been gaining momentum.
In WirelessHART, the wireless mesh network is formed based on the information indicating the communication quality that is obtained when the wireless device disposed in a field performs communication with surrounding wireless devices or wireless access point devices. For this reason, a wireless path is not determined until the wireless device is actually disposed in the field. Because the transmission delay or the consumption power of the wireless device depends on the wireless path, if the wireless path is not determined when designing a system, the transmission delay or a battery exchange period of the wireless device cannot be estimated. For this reason, when the technology used in WirelessHART is applied to the control of a plant and the like, a problem may occur in terms of real-time responsiveness and maintenance.
In WirelessHART, the wireless path is dynamically switched according to the communication quality of each wireless device, even after the wireless path is determined. For this reason, the transmission delay or the consumption power of the wireless device may momentarily change according to switching of the wireless path. In this case, the transmission delay or the battery exchange period of the wireless device cannot be estimated and a problem may occur in terms of real-time responsiveness and maintenance, similar to the above case.
As in WirelessHART, if the wireless path is dynamically changed according to the communication quality of each wireless device, the operator cannot figure out the actual wireless path. When the operator figures out the actual wireless path, the operator can plan to do the regular work (for example, work for cutting a branch of a tree that has become an obstacle of the wireless communication) or an operative rule (construction regulation of a structure that has become an obstacle of the wireless communication) that is needed to avoid communication obstacles anticipated to be generated in the future. However, when the operator cannot figure out the actual wireless path, problems occur in terms of conservativeness because the operator cannot plan to do the regular work or the operative rule.